The long term goal of our laboratory is to define gene- and cell-based strategies that restore hearing and balance in the dysfunctional inner ear. The short term goals are to advance our understanding of morphogenesis, pattern formation, and cell fate specification in the mouse inner ear. We use the mouse as a model system because an ever-expanding array of natural and induced genetic mutations exist that serve as accurate paradigms for human inner ear dysfunction. Our overarching technical approach relies on experimental embryology, a palette of surgical, imaging, microinjection and molecular techniques that permit access to the developing mouse inner ear in utero and enable genetic manipulation of precursor cells that give rise to the auditory and vestibular sensory structures. I this proposal, we aim: 1) to fate map the mouse otic vesicle in vivo~ 2) to define the types of cel fate choices otic precursors make and the timing of those choices~ and 3) to define the clonal contributions of neuroepithelial progenitors to the differentiated inner ear. A fate map describes what distinct populations of cells become as the inner ear matures. Developmental biologists use fate maps to understand how progenitor gene expression in a developing tissue or organ drives maturation and results in the acquisition of form and function. Intersection of indelibly labeled precursors with known domains of gene expression can teach us the molecular signals required to pattern sensory organs and specify cell fate. Lineage analysis, on the other hand, identifies the differentiated cells an individual otic precursor makes and reveals their location i the mature sensory organ. Clonal relationships will teach us if genetically defined pools of precursors are programmed early on in development to give rise to gross anatomical structures in the inner ear and to the sensory patches. The output of fate mapping and lineage analysis is a deeper understanding of the genetic regulation of progenitor cell identity and behavior. And that regulation promises to be far more complex that originally envisioned. Recent genetic fate mapping data show that neuroepithelial progenitor cells from the neural tube and likely the neural crest contribute precursor cells to the otic epithelium that generate sensory and nonsensory cells upon differentiation. These novel data firmly challenge the precept that the inner ear develops exclusively from placodal ectoderm and imply that neural ectoderm may uniquely participate in patterning and cell fate specification. Clonal analysis of these geneticall separable neuroepithelial precursor populations will advance our core knowledge about the embryonic origins of the mouse inner ear. A more complete understanding of the fate, lineage, and behavior of inner ear progenitor cells will inform the design of gene- and cell-based strategies aimed at the restoration of hearing and balance.